The present invention relates to a field emission display and a method of driving the same, and more particularly to a field emission display having a memory for storing a current value of a current which flows through a fluorescent power source and a correcting circuit connected to the memory for correcting an output from a cathode panel driver circuit in accordance with the stored current value.
The field emission display has received a great deal of attention as a flat and thickness-reduced advanced display in the next generation. The field emission display is attractive in view of reduced thickness for displaying dynamic images in accordance with picture signals for television broadcastings. The field emission display is attractive in view of reduced manufacturing cost for displaying images in accordance with picture signals from computer as compared to liquid crystal displays. The field emission display comprises a cathode panel for emitting electrons into a vacuum space in accordance with a principle of field emission, and a fluorescent panel for causing luminescence due to excitation energy of the emitted electrons. The above cathode panel faces is separated by a vacuum space from the fluorescent panel. The cathode panel further comprises an array of plural electron source units, each of which is capable of electron emission. The cathode panel is connected to a selecting circuit for selecting one or more electron source units to apply a voltage to the selected electron source units for causing the electron emissions from the selected electron source units. The selecting circuit may be either a simple matrix type wiring or an active matrix type circuit. The fluorescent panel is applied with a positive voltage which is higher than a cathode panel potential of the potential of the electron source units, for example, by about 5V. The above voltage applications cause electron emissions from the electron source units of the cathode panel, and then the emitted electrons are incident into the fluorescent panel, whereby a luminescence is caused on the fluorescent panel to enable the field emission display to display any images.
The field emission display of the simple matrix type has a two-dimensional matrix array of electron source units (0,0), (0,1), (0,2), (1,0), (1,1), (1,2), (2,0), (2,1) and (2,2). FIG. 1 is a diagram illustrative of the two-dimensional matrix array of electron source units of the field emission display of the simple matrix type. Each of the electron source units includes not only the electron source unit provided in the cathode panel but also a fluorescent portion of the fluorescent panel, wherein the fluorescent portion makes a pair with the electron source unit.
FIG. 2 is a timing chart illustrative of driving signals for driving the simple matrix field emission display of FIG. 1. This driving timing chart is in case of pulse width modulation. At a timing xe2x80x9cAxe2x80x9d in a first frame xe2x80x9cF1xe2x80x9d, electrons are emitted from the three electron source units (0,0), (0,1) and (0,2). Each of the electron source units corresponds to each of pixels. The each pixels comprise micro-chip cathodes. In accordance with the simple matrix field emission display, emitted electrons are then incident into the fluorescent panel, whereby the fluorescent panel shows a luminescence. A brightness of the luminescence depends on an amount of the incident electrons into the fluorescent panel and an applied voltage to the fluorescent panel. The amount of the emitted electrons depends on an applied voltage between a gate electrode and a cathode electrode as well as depends on the field emission structure and material. It is possible that under the same applied voltage condition, the amount of electron emission varies depending upon the structure, material and state of the display surface of the display device. In this case, the display quality in stability is deteriorated.
It has also been known that the carbon nanotube is utilized for the electron source. In this case, electron emission characteristics vary over time. To solve this problem, it is required to increase additional manufacturing processes or to do complicated control methods. This solution methods cause the increase in the manufacturing cost.
In Japanese laid-open patent publication No. 7-57667, a conventional field emission display is disclosed, wherein the number of micro electron emitters and micro electron transmission holes is varied so that a total current of each pixel is almost stable, and the brightness is stable over the entire display surface. The brightness is, however, not stable over time.
Japanese laid-open patent publication No. 8-69746 discloses that a conventional method of forming a field emitter, wherein an inter-electrode film for electron emission is gradually formed under control cased on a measuring result of the field emission characteristics, and an electron source having the field emitter as well as an image creating device. In accordance with this conventional technique, the field emitter is formed which shows the stable electron emission characteristics for obtaining the stability in brightness and providing high quality image. The brightness is, however, not stable over time.
Japanese laid-open patent publication No. 8-248914 discloses a driver circuit for driving the field emitter, wherein a current variation of each pixel of the display is detected to correct video signals for improvement in brightness and providing high quality image. This technique is to control the power source for causing the electron emissions so as to improve the brightness characteristics and provide the high quality image. The necessary control is, however, complicated.
Japanese patent No. 2907080 discloses a conventional field emission display, wherein a resistance layer is formed in series between a cathode wire and an emitter cone for reducing variation in amount of electron emission. This conventional technique is to adjust a resistance value over in-plane positions of the resistance layer connected in series to the cathode electrode for reducing the in-plane unstability in the manufacturing process. After the manufacturing process has been completed, it is difficult to change the resistance value over time.
Japanese laid-open patent publication No. 8-273560 discloses a display and a method of driving the same, wherein a constant current circuit is connected to a cathode electrode for reducing variation in brightness. This conventional technique is to provide the contact current circuit for suppressing the variation in brightness. Parts of the emitted electrodes from the cathode electrode enter into the gate electrode or are involved into a solid creeping conduction, thereby deteriorating the fluorescent current accuracy. This conventional technique is to provide control circuits such as transistors for individual cathode electrodes. This makes the display structure complicated.
Japanese patent No. 2970539 discloses a field emission cathode and a cathode tube using the same, wherein a resistance layer provided to the cathode electrode is formed co-axially around the cathode. This conventional technique is to provide the resistance in series, for which reason it is difficult to change or vary the resistance value after the manufacturing process has been completed.
In the above circumstances, it had been required to develop a novel field emission display having a memory for storing a current value of a current which flows through a fluorescent power source and a correcting circuit connected to the memory for correcting an output from a cathode panel driver circuit in accordance with the stored current value, which is free from the above problem.
Accordingly, it is an object of the present invention to provide a novel field emission display having a memory for storing a current value of a current which flows through a fluorescent power source and a correcting circuit connected to the memory for correcting an output from a cathode panel driver circuit in accordance with the stored current value, which is free from the above problems.
It is a further object of the present invention to provide a novel field emission display having a memory for storing a current value of a current which flows through a fluorescent power source and a correcting circuit connected to the memory for correcting an output from a cathode panel driver circuit in accordance with the stored current value, wherein the display is capable of realizing a high quality display.
It is a still further object of the present invention to provide a novel method of driving a field emission display having a memory for storing a current value of a current which flows through a fluorescent power source and a correcting circuit connected to the memory for correcting an output from a cathode panel driver circuit in accordance with the stored current value, which is free from the above problems.
It is yet a further object of the present invention to provide a novel method of driving a field emission display having a memory for storing a current value of a current which flows through a fluorescent power source and a correcting circuit connected to the memory for correcting an output from a cathode panel driver circuit in accordance with the stored current value, wherein the display is capable of realizing a high quality display.
The first present invention provides a field emission display comprising: a cathode panel having an array of electron source units for emitting electrons; a fluorescent panel distanced by a vacuum inter-space from the cathode panel; a cathode panel driver circuit being connected to the filed emission display panel for controlling electron emissions from the electron source units; a fluorescent voltage supplying device being connected to the fluorescent panel for supplying a fluorescent voltage to the fluorescent panel; a current measuring device being connected to the fluorescent voltage supplying device for measuring a current value of the fluorescent voltage supplying device; a memory connected to the current measuring device for receiving a measured current value from the current measuring device and storing the measured current value; and a correcting device being connected to the memory for receiving the measured current value for correcting control signals on the basis of the measured current value, and the correcting device being also connected to the cathode panel driver circuit for transmitting the corrected control signals to the cathode panel driver circuit.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.